The present invention is directed to non-aqueous dispersions of photosensitive polymeric microparticles. The present invention is also directed to methods of producing such non-aqueous dispersions, curable film-forming compositions containing them, and photosensitive coated substrates.
Photosensitive materials demonstrate a response to electromagnetic radiation, including infrared, visible and ultraviolet radiation as well as light amplification by stimulated emission or laser. This response can be a type of luminescence in which visible radiation is emitted by a photosensitive material after exposure, e.g., fluorescent and phosphorescent materials; in which there is a change in the wavelength of the electromagnetic radiation passing through the material, e.g., non-linear optical materials; or in which there is a reversible change in color, e.g., photochromic materials.
Aqueous dispersions of photosensitive microparticles, and waterborne film-forming compositions containing them, can demonstrate several disadvantages. For example, waterborne film-forming compositions tend to generate foam during formulation, far more so than solventborne compositions. Foaming can make application difficult. Expensive humidity controls are often needed for application of waterborne film-forming compositions, since relative humidity affects a coating's flow properties and drying rates. Choices for adjuvant organic solvents can be limited in waterborne compositions because of evaporation rates and poor compatibility with the aqueous medium. Also high surface tension of water results in difficult wetting of certain substrates. Production equipment and lines which come into contact with waterborne compositions need to be corrosion resistant. This usually involves using plastic or expensive stainless steel in the production environment. Waterborne compositions can be difficult to render acid free due to acid's stabilization mechanism in water. In waterborne coatings, it also becomes problematic to use materials having water sensitive functional groups such as epoxy groups because appearance problems such as blushing in humid environments can develop. Microorganism growth also can be a problem in waterborne compositions.
There are products that take advantage of the phenomena demonstrated by photosensitive materials, e.g., optical elements such as optical memory elements and display elements. Although products incorporating aqueous core/shell microparticles that demonstrate photosensitive properties are known, it is desirable to provide non-aqueous products in which the properties of the photosensitive materials in the microparticles can be controlled readily, so that the drawbacks of waterborne compositions can be avoided. It is also desirable that certain physical properties of the end-product, such as hardness or abrasion resistance, be controlled without adversely affecting the properties of the photosensitive materials used in such products.